Mitigation for the Construction and Operation of Libby Dam

Libby Creek
Section 1 of Libby Creek has been sampled each consecutive year since 1998, and
although the Libby Creek Demonstration Restoration Project was completed in the fall of
2001. Fish monitoring data collected from 1998 to 2001 represents the fish community prior
to project implementation. Electrofishing conducted in 1999 and 2000 were limited to single
pass catch estimates. Although mean rainbow trout densities at this site were higher for the
two years following the restoration project implementation (100.5 fish per 1,000 feet)
compared to the four years prior to implementation (69.5 fish per 1,000 feet), the differences
were not significant (p = 0.207). Similarly, mean brook trout abundance at this site before
and after project completion were slightly higher after project completion (8.8 and 10.5 fish
per 1,000 feet, respectively; Figure 26), but the differences were not significant (p = 0.350).
Juvenile bull trout were only observed in this section in 2002, with an estimated abundance
of 3 fish per 1000 feet. There is no apparent temporal trend in rainbow trout (r 2 = 0.08; p =
0.58) or brook trout abundance (r 2 = 0.07; p = 0.61) within this section (Figure 27; Table
A4).
Section 2 of Libby Creek was sampled in 1998, 2001 and 2003 (Table A4). Rainbow
trout were substantially more abundant at this section than brook trout and bull trout during
all years (Figure 28). We estimated 203, 148 and 100 rainbow trout per 1000 feet in 1998
through 2003, respectively. There was a significant negative trend in rainbow trout
abundance through time at this site (r 2 = 0.994; p = 0.048). Bull trout were observed in this
section in 1998 and 2003 (Figure 28; Table A4).
Our estimates of rainbow trout abundance in Section 3 of Libby Creek were similar
between 2000 and 2002 (Figure 29; Table A4), with no evidence that the population differed
from a stable population (p = 0.469; r 2 = 0.548) during this period, which represents
conditions at this site prior to the upper Cleveland’s Stream Restoration Project was
completed. However, the rainbow trout estimate we conducted in 2003 was substantially
lower than previous years (mean abundance 112.3 and 168.3 fish per 1,000 feet,
respectively). We did not perform any statistical analyses to evaluate fish response before
and after project completion due to lack of replication after completion. No brook trout were
observed at this site. Estimates of juvenile bull trout abundance at this site ranged from 3 to
10.8 fish per 1000 feet over the four years (Figure 29).
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